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The Roving Brewer: Episode 3

December 15, 2006 at 12:00pm

Author(s): Eric Watson

This is the third in a series of discussions with our roving brewing expert, Eric Watson. Episode 1 of The Roving Brewer caused quite a stir and brought up a number of questions. We are addressing those question in the next several episodes.

Q: I don't understand how you can over-oxygenate the wort/starters using pure O2.

A:Actually, this is incredibly easy to do with a gas stone since it produces very fine bubbles. The majority of oxygen uptake required by yeast takes place within 10 minutes! If you left the oxygen on this long, you would definitely over oxygenate the wort and in a starter you would kill alot of the cells.

As far as homebrewers not being able to apply the mash technique, I disagree strongly. These concepts are NOT brewing system volume dependant. If you seem unable to do this it is either that your mash tun heat loss is too high, pH is wrong, milling is too coarse or your grain has degraded in it's extract/enzymatic capability. It could also be a blend of these factors.

Q: You said "... step the yeast culture up one day at a time to 100 ml, 200 ml, 400 ml, 800 ml and finally to 1,000 ml (5 total days of stepping) using a 5 deg. plato hopped wort ... aerate 24 hours a day."

Should I start with 100ml, regardless of the size of my yeast sample? E.g., would I treat a dry yeast packet the same as Wyeast smack-pack (which I presume I would wait until swollen before moving it to the 100ml starter), and the same as a yeast sample from a beer bottle?

A:My directions were aimed at starters for fully activated smack packs. If you are doing actual culturing (starting with a single cell, not repitching trub or bottle sediment), you start with 10 ml & the step to 100 and so on.

Dry yeast should only be 1) hydrated in warm water without stirring for 15 minutes, then stirred vigorously and let set for an additional 10 minutes, then added directly to the wort. They only need water and a small amount of O2. As long as they are not too old, dry packs have a very high cell count to counter their low viability.

For smack packs: Once fully activated, pitch them into a STERILE, not sanitized flask and add 100 ml of 5 deg. hopped wort. Step up as directed every 24 hours. Obviously, the final volume will well exceed 1,000 ml, I was referring only to the wort additions with those instructions. The final volume will require a vessel that can hold at least 2,500 ml with a headspace.

Q: Do I make an entire liter of 5degPlato wort, and draw off the amount that you indicated for each day to add to my starter? Or do I check the gravity of the starter each day and then add the necessary amount to adjust the total volume of the starter back up to the 5degPlato (this will no doubt require adjustments in specific gravity for each addition)?

A:No. Yeast samples from a bottle should only be cultured by harvesting a single cell from an agar plate. The reason is that you don't know exactly how long the yeast has been under the beer which is VERY stressful on the little buggers. This can lead to very poor fermentatin results if you try to simply step up the lees from the bottle. (by the way, did you know that many commercial producers condition with yeast that is different from that that the beer was fermented with? This is VERY common with ales since they cannot condition under refrigeration. Particularly among Belgian beers, lager yeast is used for this reason as well as better, faster and tighter sedimentation. If you are sure the yeast in the bottle is the fermentation yeast, by all means, culture it, but I wouldn't use the lees.)

A:No, each addition of wort is at the volume indicated. Ie... add the activated smack pack to 100 ml of hopped wort... after 24 hours, add 200 ml of the hopped wort to that and so on...

Q:How much should the starter be hopped (IBUs), and do you recommend a certain variety, or does that depend on the recipe for which the starter will be used? Bittering or aroma hops?

A:If you make 2500 ML of sterile wort for the step up process, add .25 tablespoon of a high alpha hop. The only reason that you add hops is for their anti-microbial properties. At this level, there will be no effect on the beer into which the culture is pitched. Hint: The easy way to produce sterile wort for starters is to use DME, hops, canning jars and a pressure cooker for 20 minutes at 1 bar/15 psi.

Q: How crucial is the temperature for making a starter, i.e., do I need to worry about evaporative cooling if the room temperature gets up into the mid 70's? I assume that with the starter comprising just 5% of the 5-gallon batch, and being mostly yeasties, at that, (as opposed to fermenting alcohol, and esters). Does the temp matter if we are starting lager yeast or ale yeast?

A:70~72 degrees is fine. The yeast character will not be affected in the reproductive stage at this temperature. It is fermentation temperature you want to control.

Q: What about filtering the air being pumped into the starter...how crucial do you think that this extra precaution is?

A:You can get a .45 micron, inline air filter (~$ from any larger homebrew supplier such as Beer, Beer & More Beer, Williams Brewing, Northern Brewer or possibly your local supplier. Crutial?... MANDITORY!!! You will be pumping air into this baby for days! If you try this unfiltered, you will culture everything that will eat sugars in your house!!!

The discussion continues! We will pick up with more questions in the next installment.